In wireless local area networks (LANs), a network time reservation mechanism is employed to prevent medium access contention that might otherwise arise due to the inability of all nodes in the network to properly detect the presence of transmissions from all other nodes within the network. This problem is commonly known as the hidden node problem. In the hidden node situation, a hidden node is unable to receive some or all of the transmission from another node. Thus, the hidden node may incorrectly perceive the network as being in an idle state when, in fact, the network may be busy. Hidden nodes can be caused by a variety of mechanisms including, for example, distance, presence of interference sources, partial rate/modulation incompatibility, noise and other mechanisms. When a hidden node incorrectly determines that the network is idle, the hidden node might attempt its own transmission, thereby causing a collision. While collisions are a natural, acceptable part of some networks, arising naturally in some methods for arbitrating access to the network, collisions are generally not expected to occur once the arbitration phase of network access has ended. In this regard, hidden nodes and the potential for collisions that hidden nodes introduce are detrimental to the most efficient operation of the network. To avoid hidden node collisions and the network efficiency losses created by hidden node collisions, various schemes have been introduced including a network reservation mechanism.
However, it may not always be possible to predict, at the time the reservation is requested, the amount of time required to complete the full set of frame transmissions and/or exchanges. The time can be variable due to many factors including, for example, incomplete knowledge relating to the number of frames available for transmission in the sequence when the sequence is initiated (e.g., the availability of frames for transmission may change during the transmission), incomplete knowledge relating to the specific characteristics of the frames that will be transmitted during the sequence (e.g., rate and frame lengths), and possible retransmission overhead (e.g., in case of transmission failures). Because of the possible lack of ability to predict the expected duration of the upcoming extended sequence of frame transmissions and/or frame exchanges, the initial reservation may be made with a conservative value (i.e., inclusive of some time beyond that which might be otherwise necessary), or possibly be made with a fixed value, in the case when very little knowledge is known about the number and length of frames that could be included in the sequence. Such a reservation mechanism may, in all likelihood, include more time than necessary to complete the transmission sequence, resulting in a loss of efficiency in the use of the communication medium.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of ordinary skill in the art through the comparison of such systems and methods with at least some aspects of present invention as set forth in the remainder of the present application with reference to the drawings.